Hollow fibers or microtubes of different materials can be used in many applications, depending on the hollow fiber material properties. Hollow fibers can be used in mass transfer devices, if the walls of the hollow fibers are permeable, and as heat transfer devices if the walls of the hollow fibers are heat conductive. Because hollow fibers are small, their thin walls pose relatively little barrier to heat and mass transfer between the inside and outside of the hollow fiber. It also becomes possible to package a large surface area for heat and mass transfer in relatively small volumes by densely bundling multiple hollow fibers into small packages. Examples of hollow fiber bundles used in heat and mass transfer include commercially available blood oxygenators which comprise a mass transfer portion with gas permeable hollow fibers, and a heat transfer portion with a heat conducting hollow fibers.
The forming of hollow fiber bundles presents a number of challenges. Applicant's U.S. Reissue Pat. No. RE 41,870 describes a method for forming hollow fibers using a dissolvable core and a method for forming hollow fiber bundles. Applicant's U.S. patent application Ser. No. 12/915,262, filed May 12, 2011, provides another method for forming hollow fibers and for forming hollow fiber bundles. The entire contents of each of these patents and applications incorporated herein by reference, as some of the methods and descriptions therein may have utility in the present application, or may be useful in combination herewith.
Hollow fiber bundles can be easily formed by winding, packing, layering, or assembling woven, knitted, or other structured mats of hollow fibers. One advantage of using hollow fiber mats is that the spacing between adjacent hollow fibers can be controlled to ultimately achieve a desired performance goal for the hollow fiber bundle or array such as packing density or void fraction.
Hollow fiber mats can be knitted, woven, or otherwise structured such that the hollow fibers are spaced at regular or irregular intervals, with the hollow fibers being held in place by one or more inserted transverse fibers, also known as warps. In textile terms, the hollow fibers are the weft. These warps are typically multifilament yarns or the like, monofilaments, tapes, etc. However, prior art warps used in hollow fiber mats perform no heat, mass, or energy transfer function; the only function performed is to maintain controlled placement of the hollow fibers in the mat, which ultimately controls of placement of the hollow fibers in the formed bundle.
Since the warps are in direct contact with the outside surface of the hollow fibers, the warps can inhibit the performance of the hollow fibers by blocking a portion of the hollow fiber surface area, thus reducing the effective surface area available for transfer. In biological liquid contacting applications such as blood oxygenation, the warps can act as potential thrombogenic sites which can exacerbate blood clotting in the bundle; blood formed elements and proteins can deposit on and in the warps, as well as in between the warps and the hollow fibers. Similarly, in other hollow fiber applications such as wastewater processing, bioreactors, liquid contactors, and gas separators, there is the potential for a component in a fluid within the hollow fiber bundle to be adsorbed, deposited, and trapped on the warp(s), or interact negatively with the warp(s), thus reducing the performance of the hollow fibers and compromising the bundle performance.